The present invention concerns devices for the anterior fixation of the spine. In particular, the present invention relates to a plate for the fixation of thoracic or lumbar vertebra. The plate of the present invention has particular application in situations where vertebral body corpectomies are performed, such as burst fractures with significant spinal canal compromise or vertebral body tumors.
Fractures of the spine commonly occur at the thoracolumbar junction, and particular in the T-11, T-12, L-1 or L-2 vertebrae. In the past, treatment of burst fractures involved prolonged bed rest in a body cast and/or a brace. Harrington rods were the first widely successful devices implementing internal fixation for treatment of a vertebral burst fracture. The Harrington rods involved posterior distraction of the spine and allowed some reduction and restoration of vertebral height by means of distraction. However, the inability of Harrington rods to reduce a kyphosis or to clear the spinal canal completely were major disadvantages of this approach.
To improve reduction, posterior distraction systems were modified with the use of contoured rods, sleeves for the rods, improved hooks and sublaminar wires. However, with these posterior distraction systems, it was usually recommended that the spinal fusion include 2 vertebral levels caudad to the fracture and 2 or 3 levels cephalad to the fracture. The posterior approach, even to this level of advancement, was still less than an optimum solution to the problem of treatment of thoracolumbar burst fractures.
In the early 1980's an anterior approach was developed for treatment of burst fractures. Improved scanning techniques allowed visualization of bone fragments that were present with burst fractures, so that attention could then be directed toward complete decompression of the canal as a way to provide the best environment for neurological recovery. Various fixation devices have been developed since that time based upon this theory of internal anterior treatment of burst fractures. However, the anterior approach has in some cases lead to increased operative morbidity due to the very difficult nature of the procedure. In addition risk to the vascular network as well as complete clearance of the spinal canal has been a problem with many of the anterior fixation approaches. Most of the prior internal anterior systems suffer from a great degree of complexity.
One such system is the Kanada device marketed by Acromed, Inc. of Cleveland, Ohio. The Kanada device utilizes vertebral body staples through which fixation screws are placed into the vertebral body. Rods are then engaged between the screws in the superior and inferior vertebral bodies. Normally two screws are placed in each body, therefore requiring two rods between the vertebrae. The rods are threaded at their ends to allow compression and distraction.
Another device marketed by Zimmer, provides an anterior spinal fixation system indicated for treatment of tumors or thoracolumbar burst fractures. This device is described in the patent to Dunn, U.S. Pat. No. 4,289,123, which issued on Sep. 15, 1981. This device is similar to the Kanada device in that it uses rods between the superior and inferior vertebrae. A pair of large plates contoured to the vertebrae are engaged by way of a number of screws.
Several plating systems have been developed for anterior internal fixation of the spine. One of these plates, the Syracuse I-plate provides a number of differently sized I-shaped plates which are engaged across the burst fracture. However, the Syracuse I-plate does not allow for compression or distraction of a bone graft between the superior and inferior vertebrae.
Acromed Inc. markets a contoured anterior spinal fixation plate (CASF.TM. plate) which is indicated for treatment of lumbar burst fractures and tumors. The plate includes a number of screw openings through the contoured plate. The number of openings simply provide different locations for engaging a bone screw to the vertebra, and does not lend itself to compression or distraction of a bone graft. Duma International of Taipai, Taiwan, offers the Stafix plating system which includes a plate that has a number of screw holes and a single screw slot. The Stafix plate permits quadrilateral placement of bone screws, but is not readily adapted for compression or distraction. Moreover, this plate, as with the aforementioned anterior plates, lack the ability to provide rigid or semi-rigid fixation using bone screws or bone bolts.
Even with these prior anterior internal fixation systems, there remains a need for a plate and screw system for the efficient management of thoracolumbar burst fractures and tumors. There is a need for such a system which permits anterior load sharing, as well as compression and distraction. The system must also be easy to implant, to thereby reduce operative morbidity.